Aluminum-zirconium compounds are well known as effective antiperspirants. The presence of zirconium species however, decreases the stability of the corresponding aluminum-zirconium antiperspirant solutions because zirconium hydrolysis species precipitate at a relative lower pH than the polymeric aluminum species. An amino acid, such as glycine, is added to stabilize the corresponding aluminum-zirconium antiperspirant solution. The coordination between zirconium and glycine stabilizes the zirconium species from gelling up in aqueous solution. Various patents are known that reference commercial aluminum-zirconium-glycine salts (ZAG) and compositions contain glycine, with the Zr:glycine weight ratio being approximately 1:1. While not wishing to be bound by a specific theory, it is believed that the addition of glycine decreases the efficacy of the corresponding aluminum-zirconium antiperspirant because of the coordination between zirconium and glycine.
U.S. Pat. Nos. 4,775,528; 5,114,705; 5,225,187; 5,486,347; 5,589,196; 5,955,064; 6,066,314; 6,074,632; EP 0 653 203 A1, for example, disclose antiperspirant compositions containing both glycine and polyhydric alcohols. As has been described in co-pending U.S. patent application Ser. No. 10/185,299 filed on Jun. 28, 2003, a stable and highly effective aluminum-zirconium antiperspirant solution is obtained by eliminating glycine and introducing polyhydric alcohol. While the introduction of polyhydric alcohol to aluminum-zirconium antiperspirant solution without glycine increases the efficacy of the antiperspirant, it also tends to introduce an undesirable tackiness to the corresponding antiperspirant active. Thus it is highly desirable to have a stable and effective aluminum-zirconium solution not only free of glycine but also free of polyhydric alcohol.
U.S. Pat. No. 2,906,668 to Beekman described aluminum-zirconium antiperspirants made by heating a zirconium salt compound with a source of aluminum hydroxychloride for a long period; or by heating a zirconium oxychloride with an aqueous solution of aluminum chloride and aluminum metal until reaction is complete. Both methods involve the employment of the heat treatment and the formation of gel during the preparation. The formation of the gel during the process of making usually results an antiperspirant composition that is less effective.
U.S. Pat. No. 2,854,382 to Grade related to an aqueous composition consisting from about 5% to about 30% by weight aluminum-zirconium salt and from 0% to 17% by weight of amino acid. It is mentioned in the patent that the amount of amino acid added is directly related to the concentration of the aluminum-zirconium salt. About 17.5% by weight of amino acid is required for a 30% by weight of aluminum-zirconium solution and about 11.5% by weight of amino acid is needed for a 20% antiperspirant salt solution. In fact, the inventors have found that when the concentration of the salts is about 10% or less by weight, no amino acid is required to prevent gelling of the solution. It is believed, however, that the zirconium species polymerize substantially in the dilute aluminum-zirconium that results in a decrease in efficacy of the corresponding antiperspirant solution. It is highly desirable to provide a stable and concentrated aluminum-zirconium antiperspirant solution that is both very effective and economical to produce.
We have now discovered that under two circumstances a stable aluminum-zirconium antiperspirant solution can be made at room temperature (RT). First, at low metals/chloride (M/Cl) atomic ratio, i.e., from about 0.9 to about 1.25, an aluminum-zirconium tetrasalt solution is prepared with excellent stability. Second, at higher Al/Zr atomic ratio, i.e. from about 6 to about 10, stable aluminum-zirconium octa and penta salt solutions are formed. Under both conditions the aluminum-zirconium antiperspirant solutions showed excellent stability.
Accordingly from the standpoint of providing a more economical while very efficacious antiperspirant and from the status of the known prior art, it is desirable to provide a stable aluminum-zirconium antiperspirant composition that possesses a high active content, that does not require the inclusion of amino acid or polyhydric alcohol.